<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<style>

#a {
  -moz-column-count: 2;
  -moz-column-width: 100px;
  float: left;
  border: 2px solid magenta;
  height: 200px;
}

#b {
  -moz-column-count: 2;
  -moz-column-width: 100px;
  float: left;
  border: 2px solid green;
  height: 300px;
}

</style>
</head>

<body onload="document.getElementById('span').style.display = '-moz-inline-grid';">

<div id="a"><div id="b"></div><optgroup label="foo"><span id="span"></span></optgroup></div>

</body>
</html>
